Modern imaging methods are frequently used to create two- or three-dimensional image data, which can be used to visualize an imaged examination object and also additionally for further applications.
Imaging methods are frequently based on the acquisition of X-rays, wherein so-called projection-scan data is created. For example, projection-scan data can be acquired via a computed-tomography system (CT system). With CT systems, typically a combination of an X-ray source and an oppositely arranged X-ray detector arranged on a gantry rotate about a scanning chamber in which the examination object (hereinafter referred to, without restricting the generality, as the patient) is located. In this case, the center of rotation (also called the “isocenter”) coincides with a so-called system axis z. The patient is irradiated with X-rays from the X-ray source during one or more rotations, wherein projection-scan data or X-ray projection data is acquired via the oppositely located X-ray detector.
X-ray detectors used for CT imaging generally comprise a plurality of detection units, which are usually arranged in the form of a regular pixel array. The detection units in each case create a detection signal for the incident X-rays on the detection units with said signal being analyzed at specific time points with respect to the intensity and spectral distribution of the X-rays in order to obtain conclusions regarding the examination object and to create projection-scan data.
Other imaging techniques are, for example, based on magnetic resonance imaging. During the creation of magnetic resonance images, the body to be examined is exposed to a relatively high basic magnetic field, for example 1.5 tesla, 3 tesla, or in newer high magnetic field systems even 7 tesla. Then, a suitable antenna facility is used to emit a radio-frequency excitation signal which causes the nuclear spins of certain atoms excited into resonance by this radio-frequency field in said magnetic field to be tilted by a specific flip angle relative to the magnetic field lines of the basic magnetic field. The radio-frequency signal, the so-called magnetic resonance signal, radiated by the nuclear spins during relaxation is then received by suitable antenna facilities, which can also be identical to the transmitting antenna facility. The raw data acquired in this way is used to reconstruct the desired image data. For spatial encoding, during transmission and reception of the radio-frequency signals, the basic magnetic field is in each case superimposed by defined magnetic field gradients.
Patients have to be positioned in different ways for different types of imaging examination. For example, during CT imaging, to reduce the radiation dose, the patient's arms should be positioned above the head when the abdomen or thorax is to be scanned. On the other hand, it is advisable to position the arms pointing toward the feet when images are to be recorded of a patient's head. If images are to be depicted of a patient's extremities, other positions for the patient's body are specified. Therefore, it is important to know which relative position individual body parts of the patient should adopt for medical imaging. The specifications may vary in different hospitals, but should in particular be determined by the constitution of the respective patient if the patient is insufficiently mobile to adopt an ideal body position or is uncooperative and has to be secured. As a result, there is a large number of possibilities for positioning a patient so that medical staff are faced with a general positioning problem.
When positioning patients for medical imaging, it is inter alia also important for the axes of symmetry of the body to be correctly aligned relative to an imaging facility. As a rule, it is attempted to keep the axes of symmetry of the body as axes of symmetry in the medical image recordings as well so that they can also be identified on the images and used to identify any symmetry-breaching pathologies without laborious reworking of the images, i.e. restoration of the axes of symmetry by three-dimensional reformatting. Therefore, there is a problem with observing symmetry during the positioning of a patient for recording a medical image.
For example, when recording a CT image of a skull, the plane between the left and right halves of the skull is preferably arranged perpendicular to the CT slice plane, wherein ideally the nose points exactly upward or perpendicular to the surface of a recumbent patient. With such positioning, a hemisphere of the brain is in each case found in each axial slice of the CT image recording on the left and right half of the image as long as this does not contain any pathology that disrupts this. Symmetrical positioning of the patient on the patient table also facilitates the subsequent evaluation when imaging other regions of the body, such as, for example, an examination of the spine or the locomotor system.
While, conventionally, other steps during the course of a CT examination are very effectively defined by scan-protocol settings or reconstruction settings, to date, positioning has been, to a greater or lesser degree, a matter determined by the skills of the medical staff. Hence, this results in greater or lesser user-dependent deviations in positioning which can only be reduced by good training or lengthy experience on the part of users.
For correct positioning, at present operators must know how to position the patient. To ensure symmetrical positioning, a user can use a CT laser sight in or before a scanning plane.